In the uplink of a wireless communication system, the common radio resource shared among the user terminals is the total amount of tolerable interference, which is defined as the average interference over all the RX antennas. A relative measure of total interference is Rise over Thermal (RoT), i.e. total interference relative to thermal noise.
The total uplink load budget that is shared amongst all uplink users in one cell can be estimated as in Equation 1
                              L          UL                =                  1          -                      1                          RoT              tgt                                -                      L            margin                                              Equation        ⁢                                  ⁢        1            
Where LUL is the total uplink load budget, RoTtgt is the RoT target, Lmargin is the reserved load margin to deal with the inter-cell interference that is not monitored and the intra-cell interference oscillation.
The RoT level in a cell impacts the coverage and uplink (UL) capacity, i.e., a higher RoT level means a higher uplink load available for a cell but a smaller coverage. The coverage (target RoT) is limited by the Guarded Bit Rate (GBR) users and or the desired minimum required bit-rate of best effort users at the cell edge.
Uplink Load Control
The uplink load control estimates the resource utilization in terms of cell load generated by different type of traffic and channels of each cell based on measurements, such as, Rise over Thermal or Received Total Wideband Power (RTWP). The load control also determines and allocates the total usable Enhanced Uplink (EUL) load, which includes the allocated load headroom for the EUL users and the available EUL load that can be further allocated. Moreover the load control detects the congestion based on the uplink (UL) load usage. For instance, the load control detects the congestion when the measured RoT exceeds the RoT target level. FIG. 1 illustrates the following several load control schemes for handling the detected congestion.
Uplink Scheduling
The EUL scheduler is supposed to allocate the available UL load to EUL users who require higher uplink bit-rate and reduce the granted uplink bit-rate of some EUL users when the system is overloaded. In the current WCDMA-EUL system, according to the available EUL load and the bandwidth request of an EUL user, the EUL scheduler estimates an Enhanced Dedicated Channel (E-DCH) power offset and signals this E-DCH power offset to this User Equipment (UE) by the Enhanced Absolute Grant Channel (E-AGCH). The UE maps the received E-DCH power offset to a maximum Enhanced Transport Format Combination (E-TFC) it can use. The granted bit-rate depends on this maximum E-TFC. Another way to adjust the UE bit-rate is to use the Enhanced Relative Grant Channel (E-RGCH), which is used to increase or decrease the granted bit-rate in a predefined relative step.
In principle, when the measured UL load in a cell exceeds a certain predetermined threshold, e.g. the measured UL RoT of that cell exceeds the RoT target, the UL load control reduces the total usable Enhanced Uplink (EUL) load for that cell and the UL scheduler reduces the granted bit-rate of some EUL users accordingly. Because there is a large delay in this procedure, including RoT measurement delay, Node B processing delay, E-RGCH/E-AGCH queuing delay and UE processing delay etc, large RoT oscillation can occur, either higher or lower than the RoT target, and the RoT peak can last a long time before the RoT is reduced to an acceptable level. The total delay in this procedure can be several tens of milliseconds or even longer. This means that the RoT can not be efficiently controlled by means of reducing the granted bit-rate by the scheduler only. Moreover, the RoT can be decreased to a too low level and the uplink scheduler has to increase the granted bit-rate of some users slowly from a low granted bit-rate, which results in uplink resource waste.
BLER Controlling
For both Release 99 and EUL, the uplink data transmission aims at a configured Block Error Rate (BLER) target. There is an outer loop power control to ensure that the BLER target is met when the target transmit attempt is reached by adjusting the Dedicated Physical Control Channel (DPCCH) Signal Interference Ratio (SIR) target for each UE.
For some delay sensitive services (e.g. VoIP) over EUL, it is important that the configured BLER target is always met when the target transmit attempt is reached in order to fulfil the delay requirement. While for some non delay sensitive services over EUL, some variation in BLER can be tolerable, but still the BLER should not be too high to avoid performance degradation.
For service over DCH, it is required that the BLER target can be met so that the RLC retransmission probability can be kept in minimum level.
Fast Congestion Control
In order to reduce the RoT peak level and suppress the RoT peak quickly, Fast Congestion Control (FCC) was introduced. In WO/2001/080575 and US 2003/0003921 A1, it is proposed that Transmit Power Control (TPC) down commands are sent to targetable users when the measured RoT exceeds the target level. For a selected UE to be targeted by FCC,                If the TPC generated by the inner loop power control is TPC DOWN command, TPC down command is sent to this UE without changing the TPC command.        If the TPC generated by the inner loop power control is TPC UP command, FCC changes the TPC command to down and the TPC down command is sent to this UE, which is referred as the forced TPC down command hereinafter.        
When the RoT exceeds the RoT target, the FCC is triggered much faster than the scheduler, which means that FCC can decrease RoT oscillation and improve UL load utilization. The uplink scheduler will reduce the granted bit-rate of EUL users if FCC alone is not enough to suppress the RoT to the target level, e.g. the predefined minimum DPCCH SINR is hit for all users that can be targeted by FCC. According to the previous study, FCC scheme has shown considerable gain even there are RoT measurement errors and delays. Moreover, FCC can be a low cost implementation for considerable gain in future.
However, the BLER of the targeted users by FCC will increase accordingly. According to the Section “BLER controlling” above, it is preferable to only target the users with non-delay-sensitive users over EUL.
Therefore, the above prior art load control schemes have the following problems:
1. Low Uplink Resource Utilization with the Prior Art Load Control
FCC is a promising method to suppress RoT peaks, but the BLER of the targeted users by FCC may increase evidently, and there is no means to explicitly control the increased BLER due to the adoption of FCC. This results in quite conservative use of FCC even with FCC enabled. On the other hand, still to quite some extent we need to rely on the prior art load control and scheduler to control the uplink load and RoT, however, as mentioned in section “Uplink scheduling” the large delay in the load control and scheduler will still result in insufficient uplink load utilization.
2. The RoT Target is Conservatively Configured to Ensure the Coverage of the Worst Case
With a high RoT target, the system can benefit from the high load utilization but the system can suffer coverage problem. With a low RoT target, the system has good coverage but bad capacity.